The present invention relates to an axial air-gap rotor suitable for use as a silent call mechanism for a portable communication device and the like, and improvement of an axial air-gap motor having such a rotor. More specifically, the present invention relates to a motor providing both high speed rotation and a relatively long life.
A type of silent call mechanism for a portable communication device is a vibration motor that uses centrifugal vibrations. One such vibration motor has, on an output shaft of a regular rotation type cylindrical motor, an eccentric weight having a ginkgo leave-like cross-section. Further, the applicant has proposed an axial air-gap flat motor wherein a rotor incorporated therein generates centrifugal vibrations. A vibration motor with a rotor incorporated therein requires no output shaft and, therefore, in recent years, because of its rotation method, such motors have been used commercially as shaft-fixed types that require one fewer bearing. Such shaft-fixed type motor usually makes use of a thickness of a magnet to provide a burring hole in a bracket. A shaft base end is press inserted therein, and the other end of the shaft is received by a case, as described, for example, in Japanese Patent No. 3261329.
Further, the applicant has proposed a motor configured such that a burring hole is provided in a case. A shaft base end is press inserted therein, and the other end of the shaft is freely provided without any support, as disclosed in Japanese Patent No. 2872623.
Most of such axial air-gap motors employ an axial sliding contact type rectifier for purposes of minimization.
In such an axial sliding motor, generally a commutator comprising a plurality of segments printed on a printed wiring board and plated with a noble metal to a thickness of some μm, used in combination with an axial sliding contact brush in a plate-like shape with a thickness of 0.04 mm to 0.06 mm. When an axial sliding motor is used for a vibration motor serving as a silent call mechanism for a portable communication device, such a motor used only for alarm is operated only some 10-odd times a day (a minute or two in total), and for that reason a relatively short life is sufficient. However, when such a motor is used for games and other functions requiring vibrations, a much longer life is required.
For this reason attention has focused on the used of a cylindrical commutator, which allows thick segment pieces to be used.
While in accordance with prior art in which a cylindrical commutator is used for an axial air-gap motor, such a motor is problematic in minimization because a commutator is attached at a later time, as described, for example, in Published Japanese Patent No. H07-85636 (Japanese Patent No. 2134716).
Generally, for an axial air-gap motor, or more specifically a flat rotor, attaching a cylindrical commutator at a later time is not desirable, because rotor thickness increases, and at minimum, a thickness of 3.5 mm is required for the motor as a whole. Thus, by constructing a cylindrical commutator from a rotor itself will enable the motor thickness to be 3 mm or less.
Further, such a flat rotor generally employs a constitution in accordance with which a plurality of wound air-core armature coils are placed on one side of a printed wiring board, and a commutator is provided on the side opposite the air-core armature coils, i.e., facing the axial air-gap magnet.
However, even with a thin printed wiring board, because of copper foil, resist and the like, its thickness is about 0.2 mm. Therefore, despite the fact that the gap between such board and the axial air-gap magnet with which it is to be used is usually 0.2 mm, because the printed wiring board requires the space for its thickness, the effective air-gap until the coils increases to 0.4 mm, so that the effective air-gap magnetic flux density of the wound air-core armature coils decreases, and efficiency degrades.
It is an object of the present invention to dispose a printed wiring board in a manner such that the effective air-gap magnetic flux density contributing to coils is not lowered, and to form a commutator base using resin constituting a part of a rotor, thereby achieving a low profile by directly attaching commutator pieces to the rotor, and achieving long life by increasing a thickness of rectifier sliding contact portions.